Saccadic Oscillations that Simulate Nystagmus

may also be seen with other neurological conditions (e.g., hydrocephalus, acute febrile illness), trauma, and rarely with congenital retinal dystrophies,604 septo-optic dysplasia,129 Chiari malformation,604 and syringobulbia.192 Strabismus, most commonly exotropia, is common in children with seesaw nystagmus.184,604 The finding of null-point torticollis suggests the possibility of an associated ocular tilt reaction.40

Pendular seesaw nystagmus is most often described in patients with achiasmia37,38 or large parasellar tumors.256 It has also been reported with visual loss,382 retinitis pigmentosa,61 traumatic bitemporal hemianopia,186 and septo-optic dysplasia.129 Jerk seesaw nystagmus (hemi-seesaw nystagmus) usually occurs in patients with lesions in the region of the interstitial nucleus of Cajal.256 Such patients may also have a contralateral ocular tilt reaction.366 However, hemi-seesaw nystagmus has also been reported in patients with lesions involving the medulla,103 Chiari malformation,605 and oculopalatal myoclonus. It therefore seems likely that visual loss activates the recalibration mechanism for eye movements that compensate for head roll, and that certain mesodiencephalic or medullary lesions disrupt visual motion calibration of the normal physiological response.366

Drugs and medications such as alcohol,207 baclofen,99 and clonazepam99 have been reported to abolish seesaw nystagmus.

of convergence-retraction nystagmus with dorsal midbrain syndrome (which results from a lesion of the posterior commissure) gives strong localizing value to the dorsal mesencephalon­ . Dorsal midbrain syndrome in infancy suggests the diagnosis of aqueductal stenosis, while its recurrence­

in children who have had a ventriculoperitoneal shunt placed for hydrocephalus usually signifies shunt failure.117 The onset of dorsal midbrain syndrome in an older child suggests pineal tumor. Midbrain vascular malformations or traumatic injury may also cause dorsal midbrain syndrome in childhood.365,531 We have observed convergence-retraction nystagmus as the presenting sign of Leigh’s disease in a 4-year-old boy, and Plange450 has documented a similar case.

The finding of jerky convergent movements of the eyes on attempted upgaze in association with bilateral fixed downgaze and bilateral ptosis (rather than lid retraction) is highly suggestive of congenital fibrosis syndrome. In this setting, the apparent convergence-retraction nystagmus may be either by aberrant innervation or by the secondary adducting effects of tight inferior rectus muscles and the contracting superior rectus muscles during attempted upgaze.83

Saccadic Oscillations that Simulate Nystagmus

Convergence-Retraction Nystagmus

Convergence-retraction “nystagmus” is a disorder in which attempted upward saccades evoke repetitive, simultaneous saccadic contractions of all rectus muscles, producing a series of rapid, jerky convergent movements with associated retraction of the globes. In some patients, convergence retraction nystagmus seems to be a saccadic disorder, consisting of asynchronous opposing adduction saccades whenever upward quick phases are stimulated.365,432 In others, a vergence disorder is suggested by synchrony of the vergence response in both eyes.461

Convergence-retraction nystagmus is seen almost exclusively in the setting of dorsal midbrain syndrome, which is characterized by impaired upgaze, upper lid retraction (Collier’s sign), pupillary dilation with light-near dissociation, and impairment of either convergence or divergence.365 Infants with dorsal midbrain syndrome from congenital hydrocephalus may display the “setting sun” sign, in which upper lid retraction and an upgaze palsy occur together with tonic downward deviation of the eyes. Convergenceretraction nystagmus is best elicited by having a child follow downward-moving optokinetic targets that necessitate repetitive upward saccades. It may be overlooked if only vertical pursuit movements are examined. The invariable association

Opsoclonus and Ocular Flutter

Opsoclonus is a striking ocular motility disorder characterized by involuntary, chaotic bursts of multidirectional, high-ampli- tude saccades, without an intersaccadic interval.497 Opsoclonus differs fundamentally from nystagmus in that the oscillations are saccadic and not rhythmical and consist of long silent periods punctuated by intermittent bursts of activity. In opsoclonus, three-dimensional eye movement recordings show a combination of horizontal, vertical, and torsional eye movements in adult opsoclonus.587 Although opsoclonus has a fairly characteristic clinical appearance, Leigh and Zee365 have emphasized the uncertainty in diagnosing opsoclonus without eye movement recordings because it is impossible to ascertain the pattern of back-to-back saccades with no intersaccadic interval by mere clinical observation. When the oscillations are clinically horizontal, they are termed ocular flutter.93,365 While continuous and intermittent forms of opsoclonus seem to correlate with the severity of the underlying disease, the presence of opsoclonus versus ocular flutter does not.93

Causes of Opsoclonus

Neonatal Opsoclonus

Neonatal Opsoclonus is now a well-recognized phenomenon. Hoyt et al have reported that opsoclonus may occur as a transient phenomenon in healthy neonates.296,407 In one study,